Rotor masts for rotorcraft such as helicopters must often conform to strict tolerance requirements. As a result of fabrication errors or accidents during manufacturing, assembly, maintenance, or transport, a mast's bearing journal may become damaged and unsuitable for use. As an example, during installation of a mast into a rotorcraft, the bearing journal must make a tight precision fit and the surface of the journal may become scratched during insertion. The journal surface may also become damaged during operation, as a result of fretting, for example. In some applications and for some designs, available repair techniques are not considered adequate to restore a damaged bearing journal of a rotor mast to operating condition, and protocol often calls for a damaged mast to be discarded entirely. Therefore, it would be desirable to provide improved methods of repairing surfaces of rotorcraft masts and other precision rotary components of aviation and aerospace propulsion systems.
In some instances, bearing journals of rotorcraft gears and shafts are repaired by electrodeposition followed by a post plate bake. Copper plate or thin copper plate layered over sulfamated nickel plate is deposited onto a damaged or worn surface of a bearing journal using electrodes. During electrodeposition, a process known as hydrogen embrittlement may occur wherein hydrogen atoms dissolve into the metal matrix of the mast causing excessive internal stresses. Because the internal stresses may later induce cracking, the post plate hydrogen embrittlement bake of the mast or gear is required to remove the dissolved hydrogen. However, post plate hydrogen embrittlement bakes can have a detrimental outcome for some mast designs and mast applications. For example, some rotorcraft masts contain electronics that may be destroyed by the high temperatures of a post plate hydrogen embrittlement bake. Especially in rotor designs where the electronics cannot be replaced without compromising the integrity of the rotor mast, this situation often requires the mast to be replaced entirely. Thus, a need exists for new methods of repairing helicopter masts wherein hydrogen embrittlement may be avoided.